Unep-WCMC has produced its report, Cloud Forest Agenda, with IUCN-The World Conservation Union and Unesco. It is being launched at a meeting in Kuala Lumpur, Malaysia, of the Convention on Biological Diversity, which runs from 9 to 20 February.

The authors relied on satellite data to establish that cloud forests cover just under 400,000 sq km (98,840,000 acres) worldwide, less than 2.5% of the Earth's tropical rain forests.

Mark Collins of Unep-WCMC said of the report: "A key finding is that cloud forests are rarer than thought, with the true area 20% less than the previous estimate of half a million square kilometres."

The researchers found about 60% of cloud forests are in Asia, not in Latin America as had been thought. About 25% of the share is there, with the remaining 15% in Africa.

The report says: "The ability of cloud forests to strip and retain moisture from cloud and fogs is key to abundant, clean and predictable water supplies in many areas, especially during dry seasons.

"The cloud forests of La Tigra National Park in Honduras provide over 40% of the water
for the 850,000 people living in the capital, Tegucigalpa.

Genetic treasury

Apart from their utility, cloud forests are home to many species found nowehere else on Earth, including the mountain gorilla of Africa, the spectacled bear, and the resplendent quetzal, Guatemala's national symbol.

In the Mexican mist (Image: Philip Bubb)

The report says wild relatives of key food crops often grow in the forests, making them important gene pools.

Threats include farming, poaching, fires, logging, road-building and the introduction of alien species. But the authors think climate change could be the biggest danger.

Philip Bubb of Unep-WCMC, one of the authors, said: "A unique feature of these forests is that they can capture moisture through condensation from the clouds.

"If temperatures rise one degree in the lowland this equates to two degrees in the mountains and can result in the clouds lifting and the cloud forest drying out."

Antediluvian memories

Mr Bubb told BBC News Online: "Often the forests are growing at the top of the mountains, and have nowhere to retreat to from the rising temperature. And the increasing heat make the clouds rise anyway.

"My chief memory of the forests is of their stunning beauty. They're like something out of The Lord of the Rings, great tall trees covered in ferns and orchids. The birdsong echoes through the cool moist air, and they feel very ancient places."